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Four years ago, thousands of Snowy Owls stormed the northern United States, taking up posts in surroundings drastically different from the flat Arctic tundra over which they typically preside. Some whiled away the hours peering at dog walkers from suburban fences; one learned to hunt around a Minnesota brewery with mouse problems. In a typical winter, around 10 Snowies visit Pennsylvania, but in 2013 the state was graced by 400. They were part of the largest Snowy Owl irruption, or influx of a species into a place they don’t usually live, the U.S. has seen since the 1920s.

If you missed it, you might be in luck. , a volunteer-fueled Snowy Owl-tracking organization founded after that irruption, predicts another wave of Arctic raptors will hit North America this winter, according to their most recent blog .

Scott Weidensaul, one of the directors of Project SNOWstorm, says the clues point to a big irruption, but the group also fully admits there's no way to definitively know how big it could be or if it will even happen at all. “There’s a little bit of voodoo and black magic in all of this,” Weidensaul says. Though Snowy Owl migration patterns are mostly mysterious, there have been some tell-tale signs that the birds are on their way.

For one, some Snowy Owls already seem to be retracing the last irruption’s process. Data are sketchy and variable, but it appears that big southward movements occur about once every four years. That's because lemmings, their preferred prey, go through regional population explosions at about the same interval. In 2013, those little Arctic rodents had a banner year on the Ungava Peninsula in Northern Quebec, fueling a highly successful breeding season for the owls that flocked to that area. Sure enough, this past breeding season, Canadian wildlife biologists studying caribou reported an unusually high number of owls flapping around the same area, reports others have confirmed.

Early stateside migrators have also been spotted. A couple hundred have flocked to the Northeast and Upper Midwest, Weidensaul says—single birds have been spotted as far south as Oklahoma, Missouri, and North Carolina—and their numbers are building faster than they did in 2013. When more of the species catch up, SNOWstorm volunteers will know for sure if the irruption is bona fide, and where it will hit hardest.

Part of the uncertainty in predicting this year’s potential irruption stems from the lack of people monitoring Snowy Owl nests in the wilderness of northern Quebec. According to Weidensaul, nests held eight or nine eggs each in 2013—far more than the typical three to four. Those unusually large clutches contributed to the impressive numbers from a few years ago. Without an estimate of recent clutch sizes, SNOWstorm can’t predict how big this inundation could be.

No matter how many ultimately show up, these birds are tough. People often assume that if they see an Arctic bird in, say, Indiana, it must be sick or starving. In reality, these Snowy Owls are fairly fat and healthy, says Weidensaul, and will eat anything they find. That includes the Snowy found gnawing on a bottle-nosed dolphin carcass in Delaware a few years ago, fending off its find from Turkey Vultures.

Sometimes, though, the birds struggle to navigate developed landscapes full of buildings and telephone wires. Airport runways especially lure Snowy Owls in with their flat, treeless expanses, where planes taking off pose a danger, says Weidensaul. If seriously injured, the birds might need assistance, but otherwise, people shouldn't get too close. Young owls who have no experience with humans often let birders and photographers approach them; these interactions can end with the birds backing up into highways and other dangerous situations.

Weidensaul doesn’t blame people for being curious—the birds are a rare glimpse of Arctic life that deserve all of the attention. As he says, “you’re not going to see a polar bear walking through your neighborhood.”

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